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Abstract:
Abstract: Previous investigations have produced conflicting
findings regarding the effects of normal aging and Alzheimer's
disease on semantic memory. To address this issue, the present
study assessed the effects of item dominance on retrieval at two
levels of semantic representation: attributes of objects and
exemplars of semantic categories. Observers were presented with
object-attribute and category-exemplar word pairs and asked to
decide as quickly as possible whether the attribute or exemplar was
a feature of the object or a member of the category, respectively.
Young adults produced longer response latencies for low dominance
than high dominance items for both attribute and exemplar items.
Normal elderly observers displayed no effect of dominance for
attribute items, yet displayed an effect of dominance for exemplar
items comparable to that displayed by young adults. Alzheimer
patients (despite accurate responding) failed to display an effect
of dominance for either attribute or exemplar items. These results
suggest that retrieval of attributes and exemplars are in part
mediated by distinct processes, and that aging and Alzheimer's
disease produce distinct semantic memory alterations. Age-related
decreases in cortical arousal may reduce the preferential retrieval
of high dominant attributes but not affect the hierarchical
organization of semantic memory, whereas Alzheimer-related
degradation of semantic representations may cause high and low
dominant exemplars within a category to become less distinguishable
from each other.
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